There is a question of whether or such tools are legal, but as far as Germany is considered, they are. The German Supreme Court has recently dismissed a case brought by Axel Springer to ban ad blockers from being used, ultimately ruling that such tools are legal. This is despite Axel Springer claiming that such tools violate competition laws.
In a statement issued by Adblock Plus, “We are excited that Germany’s highest court upheld the right every internet citizen possesses to block unwanted advertising online.” Unsurprisingly Springer isn’t particularly happy about the verdict and there are plans to appeal the ruling to the Constitutional Court on the grounds that ad blockers violate press freedom by “disrupting online media and their financial viability”.
It is an interesting debate because even companies such as Google are getting in on the action. The company had previously announced that they would be building native ad blockers in its Chrome browser, which means that companies like Axel Springer will have more than just Adblock Plus to deal with.